I encountered an issue when building the test_progs from the repository[1]:
$ pwd
/work/Qemu/x86_64/linux-6.10-rc2/tools/testing/selftests/bpf/
$ make test_progs V=1
...
./tools/sbin/bpftool gen object ./ip_check_defrag.bpf.linked2.o ./ip_check_defrag.bpf.linked1.o
libbpf: failed to find symbol for variable 'bpf_dynptr_slice' in section '.ksyms'
Error: failed to link './ip_check_defrag.bpf.linked1.o': No such file or directory (2)
...
Upon investigation, I discovered that the btf_types referenced in the '.ksyms'
section had a kind of BTF_KIND_FUNC instead of BTF_KIND_VAR:
$ bpftool btf dump file ./ip_check_defrag.bpf.linked1.o
...
[2] DATASEC '.ksyms' size=0 vlen=2
type_id=16 offset=0 size=0 (FUNC 'bpf_dynptr_from_skb')
type_id=17 offset=0 size=0 (FUNC 'bpf_dynptr_slice')
...
[16] FUNC 'bpf_dynptr_from_skb' type_id=82 linkage=extern
[17] FUNC 'bpf_dynptr_slice' type_id=85 linkage=extern
...
For a detailed analysis, please refer to [2]. We can add a kind checking to
fix the issue.
[1] https://github.com/eddyz87/bpf/tree/binsort-btf-dedup
[2] https://lore.kernel.org/all/0c0ef20c-c05e-4db9-bad7-2cbc0d6dfae7@xxxxxxxxxx/
Fixes: 8fd27bf69b86 ("libbpf: Add BPF static linker BTF and BTF.ext support")
Acked-by: Eduard Zingerman <eddyz87@xxxxxxxxx>
Reviewed-by: Alan Maguire <alan.maguire@xxxxxxxxxx>
Signed-off-by: Donglin Peng <dolinux.peng@xxxxxxxxx>
---
v2:
- Refactored the code using btf_is_var
- Improved the comment to be more reasonable
---
tools/lib/bpf/linker.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)
diff --git a/tools/lib/bpf/linker.c b/tools/lib/bpf/linker.c
index 0d4be829551b..5a583053e311 100644
--- a/tools/lib/bpf/linker.c
+++ b/tools/lib/bpf/linker.c
@@ -2213,10 +2213,17 @@ static int linker_fixup_btf(struct src_obj *obj)
vi = btf_var_secinfos(t);
for (j = 0, m = btf_vlen(t); j < m; j++, vi++) {
const struct btf_type *vt = btf__type_by_id(obj->btf, vi->type);
- const char *var_name = btf__str_by_offset(obj->btf, vt->name_off);
- int var_linkage = btf_var(vt)->linkage;
+ const char *var_name;
+ int var_linkage;
Elf64_Sym *sym;
+ /* could be a variable or function */
+ if (!btf_is_var(vt))
+ continue;
+
+ var_name = btf__str_by_offset(obj->btf, vt->name_off);
+ var_linkage = btf_var(vt)->linkage;
+
/* no need to patch up static or extern vars */
if (var_linkage != BTF_VAR_GLOBAL_ALLOCATED)
continue;
--
2.25.1
